This sounds common:
http://www-10.lotus.com/ldd/nd6forum.nsf/55c38d716d632d9b8525689b005ba1c0/ffc7f4c0e8ac777e85256d260076a40
http://www-10.lotus.com/ldd/nd6forum.nsf/55c38d716d632d9b8525689b005ba1c0/c456febaf77d458a852571240037778
I copied the databse to local and it worked ok.
Only failed on the server.
I changed code from
set col.=source.document.responses
to
Dim unid As String
unid=source.Document.UniversalID
ss=|Form="Child" & @text($REF)="| & unid & |"|
Dim col As notesdocumentcollection
Set col = db.search(ss,Nothing,0)
not as elegant but it worked.